1. Field of the Invention
The present invention relates generally to gene sequences that encode peroxidase genes. In particular, the present invention relates to the isolation and characterization of novel gene sequences which encode the peroxidase P7X gene and promoter isolated from maize inbred line Mp307. Additionally, this invention relates to methods of controlling plant-parasitic nematodes by application of recombinant DNA technology.
2. Background of the Technology
Nematodes are slender, worm-like organisms found in the soil almost anywhere in the world. A significant amount of the world""s nematodes are plant parasitic, and are among the most devastating of the numerous pests that infest the world""s food crops. Generally, feeding nematodes have complex interactions with their host plants that last more than a month.
Each year, a majority of crop losses are caused by root-knot nematodes such as Meloidogyne incognita. Members of this genus have extensive host ranges and can parasitize monocots, dicots (eudicots), herbaceous and woody species, over 2000 different plant species in all (Hussey, 1985). Nematodes have been reported to cause crop loss equivalent to more than $6 billion in the United States and more then $100 billion around the world. (U.S. Pat. No. 5,051,255).
With root-knot nematodes, infection of the plant occurs after juveniles (J2) hatch in the soil, invade the root, and migrate intercellularly to areas of differentiation and begin to set up a feeding site in xylem parenchyma cells in the vascular cylinder (Hussey and Williamson, 1998 and von Mende, 1997). This feeding site is established by injecting glandular secretions into the root cells via the nematode""s stylet. (Bleve-Zacheo and Melillo, 1997). The nematode quickly becomes sedentary endoparasites, thereby losing its ability to reinfect. (von Mende, 1997). During this parasitism, plant cells become hypertrophic and multinucleate, which is the result of early nuclear division without cytokinesis. These multinucleate cells, called giant (nurse) cells are formed very early after infection. Eight nuclei can be found within 48 hours of nematode infection. (Wiggers, et al., 1990). The giant cells are metabolically active and serve as the nutritive source for the developing nematode. Qualitative and quantitative changes in giant cell gene expression has been hypothesized to accommodate the demands of the nematode (Bleve-Zacheo and Melillo, 1997). Thus, root-knot nematodes cannot continue to develop normally without the induction and maintenance of these giant cells. (Hussey, 1989).
Various methods have been used to control plant parasitic nematodes. These methods include quarantine measures, manipulation of planting and harvesting dates, improved fertilization and irrigation programs that lessen plant stresses, crop rotation and fallowing, use of resistant and tolerant cultivars and rootstocks, organic soil amendments, and biological and chemical control. (Atkinson, 1992) Today, most of the plant-parasitic nematodes are controlled by chemical nematicides. These compounds are generally very toxic and have been suspected of causing environmental damage. For example, nematicides such as aldicarb, ethoprop, and carbofuran have been determined to be highly toxic to mammals, birds, and fish. Because of this, and the growing concern about the possibility of ground water contamination, several nematicides have had their use restricted or rescinded all together.
Thus, there exists a long felt need for safe and effective methods of protecting plants, particularly crop plants, from infection by plant-parasitic nematodes. Biological or xe2x80x9cnaturalxe2x80x9d methods rather than methods dependent on the application of chemicals are especially important from the standpoint of economics and environmental concerns.
It is an object of the invention to provide an effective and safe means to control plant-parasitic nematodes.
It is also an object of the invention to provide a novel gene sequence which encodes the peroxidase P7X gene isolated from maize inbred line Mp307.
It is yet another object of the invention to provide a novel gene sequence which encodes the upregulated peroxidase-promoter for the peroxidase P7X gene isolated from maize inbred line Mp307.
It is a further object of the invention to provide a method of nematode resistance in plants.
It is an object of the present invention to provide nucleic acid constructs and transcription cassettes which provide for regulated transcription in plant tissue in response to nematode infection.
It is a further object of the invention to provide transgenic plants containing the nucleic acid constructs according to the present invention.